Method of continuously vaporizing and superheating liquefied cryogenic fluid

ABSTRACT

The present invention relates to a method of continuously vaporizing and superheating liquefied cryogenic fluid for an ultimate use. A stream of liquefied cryogenic fluid is passed in heat exchange relationship with a stream of ambient water so that the cryogenic fluid is heated and vaporized. The vaporized cryogenic fluid stream is divided into first and second portions and the first portion is passed in heat exchange relationship, with the input combustion air to a gas turbine engine so that the air is cooled and the power output of the turbine increased. The second portion is passed in heat exchange relationship with the exhaust gases generated by the gas turbine engine so that the second portion is superheated to a predetermined temperature level, and the first and second portions of the vaporized cryogenic fluid stream are then combined so that a stream of vaporized cryogenic fluid superheated to a desired temperature level is produced. The power output of the gas turbine is advantageously used for providing power for pumping the streams of liquefied cryogenic fluid and ambient water.

United States Patent 1 [111 3,726,657 Arenson 1March 13, 1973 METHOD OF CONTINUOUSLY VAPORIZING AND SUPERHEATING LIQUEFIED CRYOGENIC FLUID [75] inventor: Edwin M. Arenson, El Reno, Okla.

[731 Assignee: Black, Sivalls 8: Bryson, lnc.,

Oklahoma City, Okla.

[22] Filed: April 15, 1971 [21] Appl. No.: 134,159

[52] US. Cl. ..60/39.02, 60/3971, 62/52 [51] Int. Cl ..F02c 7/34, F02m 31/60 [58] Field of Search ...60/39.71, 39.02, 39.06; 62/52, 62/53 [56] References Cited UNITED STATES PATENTS 3,552,134 1/1971 Arenson ..60/39.71

3,234,738 2/1966 Cook ..60/36 3,479,832 ll/l969 Sarsten et al. ...62/52 1,310,253 7/1919 Shuman.... 60/3971 3,438,216 4/1969 Smith ..62/52 3,446,029 5/1969 Grgurich et al. ..62/52 11/1962 Australia ..60/52 Primary Examiner-Carlton R. Croyle Attorney-Dunlap, Laney, Hessin & Dougherty [57] ABSTRACT The present invention relates to a method of continuously vaporizing and superheating liquefied cryogenic fluid for an ultimate use. A stream of liquefied cryogenic fluid is passed in heat exchange relationship with a stream of ambient water so that the cryogenic fluid is heated and vaporized. The vaporized cryogenic fluid stream is divided into first and second portions and the first portion is passed in heat exchange relationship, with the input combustion air to a gas turbine engine so that the air is cooled and the power output of the turbine increased. The second portion is passed in heat exchange relationship with the exhaust gases generated by the gas turbine engine so that the second portion is superheated to a predetermined temperature level, and the first and second portions of the vaporized cryogenic fluid stream are then combined so that a stream of vaporized cryogenic fluid superheated to a desired temperature level is produced. The power output of the gas turbine is advantageously used for providing power for pumping the streams of liquefied cryogenic fluid and ambient water.

18 Claims, 4 Drawing Figures AMBIENT AMB/E-A/T Mme/2E0 2W0 WATE-E WA r52 SUPC-EHEA rc-o our-4&7 lA/Lf-T ceroaav/c METHOD OF CONTINUOUSLY VAPORIZING AND SUPERHEATING LIQUEFIED CRYOGENIC FLUID BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to a method of continuously vaporizing and superheating liquefied cryogenic fluid, and more particularly, but not by way of limitation, to a method of vaporizing and superheating a stream of liquefied cryogenic fluid wherein the fluid is vaporized by heat exchange with ambient water and then superheated by heat exchange with gas turbine engine exhaust gases.

2. Description of the Prior Art It is well known that it is economically advantageous to store and transport cryogenic fluids such as natural gas and the like in the liquid state. Commonly, such fluids are refrigerated and liquefied at the site of their production and transported while in the liquid state to areas where they are to be utilized. The liquefied fluids are then revaporized and superheated to desired temperature levels at the areas of use. The term cryogenic fluid is used herein to mean those fluids which exist in the liquid state at a temperature below about 1 50F at pressures up to about 1000 psia.

In recent years the use of liquefied natural gas as a source of fuel in areas where natural gas is unavailable has increased. Many various methods and systems for vaporizing and superheating the liquefied natural gas at the areas of use have been developed. However, in systems heretofore used for continuously vaporizing and superheating liquefied natural gas (base load systems) elaborate heating equipment and high operating costs have been required. In order to improve the economics of such base load systems, it has been proposed to utilize ambient water as the heating medium for vaporizing and superheating liquefied natural gas. The term ambient water is used herein to mean water contained in large bodies such as oceans, lakes, rivers, and the like which exist at temperature levels approaching atmospheric temperatures. However, due to the large volumes of water required and the resultant cooling of the water which is detrimental to marine life and undesirable, the use of ambient water as a heating medium for superheating and vaporizing liquefied natural gas has generally been found to be impractical. By the present invention, a method of continuously vaporizing and superheating a stream of liquefied cryogenic fluid, such as liquefied natural gas, is provided wherein ambient water is used as a heating medium in combination with the hot exhaust gases generated by a gas turbine engine to vaporize and superheat the liquefied cryogenic fluid without incurring a detrimental temperature drop in the ambient water. The cooling capacity of the cryogenic fluid is utilized to cool the gas turbine engine input air thereby increasing the power output, which turbine engine power output is advantageously used for pumping the liquefied cryogenic fluid and ambient water streams.

SUMMARY OF THE INVENTION The present invention is directed to a method of vaporizing and superheating a stream of liquefied cryogenic fluid comprising passing the stream of liquefied cryogenic fluid in heat exchange relationship with a stream of ambient water so that the cryogenic fluid is heated and vaporized, dividing the vaporized cryogenic fluid stream into first and second portions, passing the first portion of the vaporized cryogenic fluid stream in heat exchange relationship with the input combustion air to a gas turbine engine so that the air is cooled and the power output of the turbine is increased, passing the second portion of the vaporized cryogenic fluid in heat exchange relationship with the exhaust gases generated by the gas turbine engine so that the second portion is superheated to a predetermined temperature level, combining the first and second portions of the vaporized cryogenic fluid stream so that a vaporized cryogenic fluid stream superheated to a desired temperature level is produced, and utilizing the power output of the gas turbine for passing the stream of liquefied cryogenic fluid in heat exchange relationship with the stream of ambient water.

It is, therefore a general object of the present invention to provide a method of continuously vaporizing and superheating liquefied cryogenic fluid.

A further object of the present invention is the provision of a method of continuously vaporizing and superheating a liquefied cryogenic fluid stream wherein the cryogenic fluid stream is heated and vaporized by heat exchange with a stream of ambient water and then superheated to a desired temperature level by heat exchange with gas turbine engine exhaust gases so that a minimum temperature drop in the ambient water is incurred and power is provided for pumping the cryogenic fluid and ambient water streams.

Yet a further object of the present invention is the provision of a method of vaporizing and superheating a stream of liquefied cryogenic fluid utilizing ambient water wherein changes in the ambient water temperature are automatically compensated for with little or no change in the rate of liquefied cryogenic fluid vaporized and superheated.

Still a further object of the present invention is the provision of a method of continuously vaporizing and superheating a stream of liquefied cryogenic fluid which may be carried out in relatively inexpensive apparatus, the operating costs of which are low as compared to heretofore used apparatus.

Other and further objects and advantages of the present invention will be evident from the following detailed description of presently preferred embodiments of the invention when read in conjunction with the accompanying drawings.

Brief Description of the Drawings FIG. 1 illustrates, in diagrammatic form, a system which may be used for carrying out the method of the present invention,

FIG. 2 illustrates, in diagrammatic form, a preferred arrangement of heat exchange and gas turbine apparatus for the system of FIG. 1,

FIG. 3 illustrates, in diagrammatic form, a presently preferred system for carrying out the method of the present invention, and

FIG. 4 illustrates in diagrammatic form, a preferred arrangement of heat exchange and gas turbine apparatus for the system of FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings, and particularly to FIG. 1, a system for carrying out the method of the present invention is illustrated and generally designated by the numeral 10. A stream of liquefied cryogenic fluid from a conventional liquefied cryogenic fluid storage tank 12, or other source is pumped by a conventional pump 14 into an ambient water-cryogenic fluid heat exchanger 18 by way of conduit 16. The heat exchanger 18 may be a plurality of open rack water heat exchangers or other conventional heat exchangers suitable for use with large volumes of ambient water. A conduit 20 having one end disposed beneath the surface of the ambient water source is connected to one or more conventional water pumps 22. The discharge of the pump or pumps 22 is connected by a conduit 24 to the water inlet connection of the heat exchanger or exchangers 18. After passing through the exchanger or exchangers 18, the water is returned or recycled to its source by way of a conduit 26. As the liquefied cryogenic fluid stream passes through the heat exchanger or exchangers 18, it exchanges heat with the water passing therethrough thereby causing the cryogenic fluid stream to be heated and vaporized. As will be further described herein, the volume of water passed through the exchanger or exchangers 18 is controlled so that the temperature drop in the water is maintained at a minimum, i.e., 1 to 2F.

A conventional gas turbine engine 28 is provided which generates large volumes of hot exhaust gases through the combustion of fuel, such as natural gas, and combustion air. The exhaust gases generated by the gas turbine engine 28 are conducted by way of a conduit or duct 30 to a heat exchanger 32. The cryogenic fluid stream heated and vaporized in the heat exchanger or exchangers l8 exits the exchanger 18 by way of a conduit 34. The conduit 34 is connected to a pair of conduits 35 and 37 and conventional controls are provided (not shown) for dividing the vaporized cryogenic fluid stream into two portions, the first portion passing into conduit 37 and the second portion passing into conduit 35. The first portion of vaporized cryogenic fluid passes by way of conduit 37 through heating tubes disposed within the heat exchanger 32. While passing through the exchanger 32, heat is exchanged between the turbine engine exhaust gases and the vaporized cryogenic fluid stream so that the cryogenic fluid stream is heated to a predetermined temperature level. Specifically, and as will be described further hereinbelow, the temperature of the heated cryogenic fluid stream is controlled at a level such that when it is heat exchanged with the input combustion air to the turbine 28, the formation of ice from water vapor contained in the air is maintained at a minimum.

The heated cryogenic fluid exiting from the heat exchanger 32 is conducted by way of a conduit 36 to a plurality of tubes disposed within a heat exchanger 38. Combustion air is drawn from the atmosphere by way ofa conduit 40 through the heat exchanger 38 and then by way of the conduit 42 into the gas turbine engine 28. While passing through the heat exchanger 38 heat is exchanged between the heated cryogenic fluid and the combustion air so that the combustion air is cooled. As has been heretofore known, the cooling of the combustion air utilized in the gas turbine 28 is advantageous in that the power output of the turbine 28 is increased.

The second portion of the vaporized cryogenic fluid stream passes by way of conduit 35 to heating tubes disposed within a heat exchanger 46. The heat exchanger 46 is connected by a conduit or duct 48 to the turbine exhaust gases exiting from the heat exchanger 32. After passing through the heat exchanger 46 the exhaust gases are vented to the atmosphere by way of a conduit or duct 50. As the second portion of the vaporized cryogenic fluid stream passes through the heat exchanger 46 it is superheated by heat exchange with the turbine engine exhaust gases to a predetermined temperature level, and exits the heat exchanger 46 by way of a conduit 52.

The first portion of the vaporized cryogenic fluid stream exits the heat exchanger 38 and is conducted by a conduit 44 to the conduit 52 wherein it combines with the second portion of the cryogenic fluid stream passing therethrough. As will be understood, the second portion of the va'porized cryogenic fluid stream is superheated to a temperature level in the heat exchanger 46 so that the resultant combined stream passing from the system 10 by way of conduit 52 is at a desired level of superheat. From the conduit 52, the vaporized and superheated cryogenic fluid is conducted to a point of use or distribution. A portion of the vaporized and superheated cryogenic fluid passing through the conduit 52 is passed by way ofa conduit 54 to the gas turbine 28 wherein it is utilized as fuel.

The liquefied cryogenic fluid pump 14 and the water pump 22 are advantageously operated by the power output of the gas turbine 28. The pumps 14 and 22 may be connected directly to the output shaft of the turbine engine 28, or alternatively, the power output of the turbine engine 28 may operate a conventional electric generator 56 which in turn provides electric power to operate the pumps 14 and 22.

Referring now to FIG. 2, a preferred arrangement of the heat exchangers 38, 32 and 46, and gas turbine 28 is illustrated in diagrammatic form.

As shown in FIG. 2, the stream of cryogenic fluid heated and vaporized in the heat exchanger or exchangers 18 is passed by way of conduit 34 to a pair of conduits 35 and 37. A conventional temperature control assembly 39 is disposed in the conduit 37 for dividing the stream of vaporized cryogenic fluid into first and second portions. That is, the temperature controller 39 senses the temperature of the combustion air passing to the turbine engine 28 by way of the duct 42 so that a quantity of vaporized cryogenic fluid is caused to pass into the conduit 35 which brings about a predetermined air temperature with the remainder passing into the conduit 37. As will be understood, a variety of conventional control apparatus may be used for this purpose.

The first portion of the vaporized cryogenic fluid stream passes by way of conduit 35 to a bank of heating tubes 60 disposed within the turbine exhaust gas heat exchanger 32. As the vaporized cryogenic fluid passes through the heating tubes 60, it exchanges heat with the turbine exhaust gases passing on the outside of the tubes causing the cryogenic fluid to be heated to a predetermined temperature level. The heated cryogenic fluid exits the tube bank 60 and heat exchanger 32 by way of a conduit 61. The temperature of the cryogenic fluid exiting the heat exchanger 32 is controlled by bypassing a portion of the inlet stream through bypass conduit 62 having a conventional control valve 64 disposed therein. The control valve 64 is operated by a conventional temperature controller 65 disposed in a conduit 66 which controller senses the temperature of the cryogenic fluid passing therethrough. The resultant heated cryogenic fluid stream is conducted by way of the conduit 66 connected to the conduits 61 and 62 to a first bank of tubes 68 disposed within the heat exchanger 38. Inlet combustion air which is drawn through the heat exchanger 38 passes on the outside of the bank of tubes 68, and heat is exchanged between the air and the heated cryogenic fluid passing through the tubes so that the air is cooled. The temperature of the heated cryogenic fluid entering the tube bank 68 is controlled at a level such that only a thin layer of ice forms on the outside surfaces of the tubes which does not impede the flow of air over the tubes or reduce the effective heat exchange area of the tubes. For example, vaporized cryogenic fluid at a temperature of F passing through the bank of tubes 68 results in an initial outside tube wall temperature below 32F, the freezing temperature of water. As a result, water vapor contained within the air passing over the outside of the tubes condenses and freezes on the outside surfaces of the tubes. The ice builds up and heat transferred from the outside of the tubes to the inside is impeded proportionately. However, the formation of the ice reaches a state of equilibrium, i.e., when the ice reaches a thickness such that the outside surface of the ice is at a temperature of 32F, the formation of new ice stops. Thus, by maintaining the vaporized cryogenic fluid passing through the inside of the bank of tubes 68 at a temperature approaching 32F, such as a temperature of 0F, only a thin layer of ice is formed on the outside surfaces of the tubes when equilibrium is reached. This thin layer does not impede the flow of air over the tubes, or reduce the effective heat exchange area of the tubes appreciably. However, if a conventional heat exchanger is used for the heat exchanger 38 of the system with the temperature of the cryogenic fluid passing through the tubes thereof maintained at a temperature of 0F or higher, the heat exchanger would necessarily be very large. For example, for an. inlet air temperature of 85F, if the temperature of the air is reduced to the desirable temperature of from F to 40F using 0F cryogenic fluid, a very large and expensive heat exchange apparatus would be required. In order to reduce the size and cost of the exchanger 38 and at the same time maintain the formation of ice therein at a minimum, the heat exchanger 38 is provided with two or more tube banks so that the air is cooled in stages. This is accomplished by passing the heated cryogenic fluid vapor at a predetermined temperature, e.g., 0F, through the first bank 68 of tubes disposed within the heat exchanger 38. Heat is transferred from the air passing over the tube bank 68 into the cryogenic fluid, cooling the air and heating the cryogenic fluid. The thus heated cryogenic fluid passes into a header 69 connecting the tube bank 68 with a second tube bank 70 disposed within the exchanger 38. In order to recool the heated cryogenic fluid stream before it enters the tube bank 70, a quantity of liquefied cryogenic fluid is injected into header 69 by way of a conduit 72. Conduit 72 is connected to conduit 16 (FIG. I) and the quantity of liquefied cryogenic fluid injected is controlled by temperature control valve 73 operably connected to a conventional temperature controller 75 disposed in the header 69 downstream of the connection of the conduit 72 thereto. The liquefied cryogenic fluid is vaporized as it mixes with the cryogenic fluid vapor stream passing through header 69 and recools the resulting combined stream of cryogenic fluid vapor back to 0F. The temperature controller 75 senses the temperature of the combined stream and opens or closes valve 73 to increase or decrease the rate of injection of liquefied cryogenic fluid accordingly. The cooled combined cryogenic fluid vapor stream passes into the tube bank 70, and additional heat is transferred from the air passing through the heat exchanger 38 to the cryogenic fluid stream. The heated cryogenic fluid stream passing out of tube bank 70 enters header 71 from where it is conducted to a third bank of tubes 74. An additional quantity of liquefied cryogenic fluid is injected into header 71 by way of conduit 76 connected thereto and to conduit 72 to recool the cryogenic fluid vapor stream passing therethrough. Temperature control valve 77 operably connected to a conventional temperature controller 78 controls the temperature of the combined stream of cryogenic fluid by controlling the quantity of liquefied cryogenic fluid injected into header 71. The recooled cryogenic fluid vapor passes from header 71 into tube bank 74 wherein additional heat is transferred to it from the air passing through the exchanger 38. Thus, the air passing through the exchanger 38 is cooled in successive stages so that a minimum quantity of ice is fonned on the outside of the tubes. That is, the temperature of the vaporized cryogenic fluid passing through each tube bank or stage is controlled at a level approaching 32F, thereby maintaining the formation of ice on the tube banks at a minimum as well as allowing a relatively small heat exchanger apparatus to be used.

The second portion of the vaporized cryogenic fluid stream passes by way of conduit 37 to a bank of heating tubes 80 disposed within the heat exchanger 46. As the second portion of the vaporized cryogenic fluid stream passes through the bank of heating tubes 80, heat is exchanged between the turbine exhaust gases and the vaporized cryogenic fluid thereby superheating the cryogenic fluid to a predetermined level of superheat. From the tube bank 80 the superheated second portion of vaporized cryogenic fluid exits the exchanger 46 by way of conduit 52. As previously described the second portion of the vaporized cryogenic fluid stream is combined with the first portion thereof conducted from the tube bank 74 and heat exchanger 38 by way of conduit 44. The temperature of the second portion of the vaporized cryogenic fluid stream is controlled at a level such that upon combining with the first portion, a combined stream at the desired level of superheat is obtained. As previously described, the superheated cryogenic fluid is passed by way of conduit 52 to a point of use or distribution. Further, a portion of the superheated cryogenic fluid may be conducted by way of conduit 54 to the turbine 28 and is utilized as fuel in the turbine 28.

In accordance with the method of the present invention as carried out in the system 10, the ambient water heat exchangers are utilized to bring about the heating and vaporization of the cryogenic fluid stream with the superheating being accomplished by heat exchanging the vaporized cryogenic fluid stream with turbine exhaust gases. Since a large portion of the total heat load required to vaporize and superheat a liquefied cryogenic fluid stream is used in superheating the stream to a desired temperature level, the water heat exchanger heat load, water volume required and temperature drop in the water are small as compared to heretofore proposed methods of vaporizing and superheating cryogenic fluids utilizing ambient water. Further, by the present invention, the volume of water utilized may be controlled so that a minimum temperature drop is obtained, e.g., 2F. More importantly, by the method of the present invention the dual function of providing power to drive the various pumps required and providing the heat energy to superheat the cryogenic fluid stream is achieved through the use of a gas turbine engine, resulting in low operating costs as compared to heretofore used methods and systems.

Referring now to FIGS. 3 and 4, an alternate system for carrying out the method of the present invention is illustrated and generally designated by the numeral 90. Referring specifically to FIG. 3, a stream of liquefied cryogenic fluid from a conventional storage tank 92, or other source, is pumped by a conventional pump 94 into a conduit 96.-A pair of conduits 98 and 100 are connected to the conduit 96, and the stream of liquefied cryogenic fluid is divided into first and second portions by conventional control apparatus (not shown). The first portion of the liquefied cryogenic fluid stream passes by way of conduit 98 into an ambient water-cryogenic fluid heat exchanger 102. As described above for the heat exchanger 18, the heat exchanger 102 may be one or more conventional water heat exchangers. A conduit 104 having one end disposed beneath the surface of an ambient water source is connected to one or more conventional pumps 106. The discharge of the pump or pumps 106 is connected by a conduit 108 to the water inlet connection of the heat exchanger or exchangers 102. After passing through the exchanger or exchangers 102, the water is returned or recycled to its source by way of the conduit 110. As the first portion of the liquefied cryogenic fluid stream passes through the heat exchanger or exchangers 102, it is heated and vaporized by heat exchange with the ambient water.

A conventional gas turbine engine 112 is provided which is similar to the turbine engine 28 described above and which generates large volumes of hot exhaust gases. The exhaust gases generated by the gas turbine 112 are conducted by way of a conduit or duct 114 to a heat exchanger 116.

The heated and vaporized cryogenic fluid exiting from the exchanger or exchangers 102 is conducted by a conduit 118 to a pair of conduits 120 and 122. The vaporized cryogenic fluid stream is divided into a major portion and a minor portion by conventional control apparatus (not shown) with the major portion passing into the conduit 120 and the minor portion passing into the conduit 122. The major portion of the vaporized cryogenic fluid is conducted by the conduit 120 to the heat exchanger 116 wherein it is superheated to a predetermined temperature by heat exchange with the turbine engine exhaust gases passing therethrough. From the heat exchanger 116 the turbine exhaust gases are vented to the atmosphere by way of a conduit 124.

The minor portion of the vaporized cryogenic fluid passes by way of conduit 122 to a heat exchanger 126. Combustion air for the turbine engine 112 is drawn through the heat exchanger 126 by way of a conduit 128. While passing through the exchanger 126, the air exchanges heat with the vaporized cryogenic fluid stream passing therethrough and is cooled. The cooled combustion air passes by way of conduit 130 into the gas turbine engine 112. The minor portion of the vaporized cryogenic fluid stream exits the heat exchanger 126 and passes into a conduit 132 which is connected to a conduit 136. The major portion of the vaporized cryogenic fluid which is superheated in the exchanger 116 by exchange of heat with the turbine exhaust gases exits the exchanger 116 by way of conduit 134 which is connected to the conduit 136. Thus, the major and minor portions of the vaporized cryogenic fluid are recombined in the conduit 136, and the combined vaporized and superheated cryogenic fluid stream resulting from the first portion of the liquefied cryogenic fluid stream passes by way of conduit 136 into a contactor 138.

A portion of the vaporized and superheated cryogenic fluid flowing through the conduit 134 is passed by way of the conduit 166 to the turbine engine 112 wherein it is utilized as fuel.

The second portion of the liquefied cryogenic fluid stream is conducted by the conduit to an inlet connection in the contactor 138 and is intimately mixed and combined with the vaporized and superheated cryogenic fluid conducted to the contactor 138 by way of conduit 136. Heat is transferred from the cryogenic fluid vapor stream to the liquefied cryogenic fluid stream within the contactor 138 causing the liquefied cryogenic fluid stream to be vaporized and heated. The temperature of the resultant composite stream, which exits the contactor 138 by way of conduit 140, is at atemperature level below the temperature level of the vaporized and superheated cryogenic fluid stream passing into the contactor 138 by way of the conduit 136. However, as will be described hereinbelow, the superheated cryogenic fluid stream is controlled at a temperature level such that after combining with the liquefied cryogenic fluid stream in the contactor 138, a composite stream at the desired level of superheat results.

Referring now to FIG. 4, a preferred arrangement of the heat exchangers 116 and 126 and the gas turbine 112 is illustrated. As previously described, the first portion of the liquefied cryogenic fluid stream is heated and vaporized in the exchanger or exchangers 102 and passes therefrom by way of a conduit 118 to a pair of conduits and 122. The vaporized cryogenic fluid stream passing through the conduit 118 is divided into a major portion which passes into the conduit 120, and a minor portion which passes into the conduit 122. Conventional temperature control apparatus 142 is provided for dividing the vaporized cryogenic fluid stream into the major and minor portions. The minor portion of the vaporized cryogenic fluid stream passes by way of conduit 122 to a first bank of heating tubes 144 disposed within the combustion air heat exchanger 126. The tube bank 144 is connected to a second tube bank 146 by a header 148, and the second tube bank 146 is connected to a third tube bank 150 by a header 152. Quantities of liquefied cryogenic fluid are injected into the headers 148 and 152 by means of conduits 154 and 156 connected thereto and connected to a conduit 158. The conduit 158 is connected to the conduit 96 (FIG. 3). Temperature control apparatus 160 and 162 function in the same manner as described above for the heat exchanger 38 of the system to control the temperature of the cryogenic fluid vapor passing through "stream passes through a tube bank 164 disposed within the heat exchanger 116 wherein it is superheated to a predetermined temperature level by exchange of heat with the turbine exhaust gases passing through the exchanger 1 16. The superheated major portion exits the exchanger 116 by way of the conduit 134 and passes into the conduit 136 where it combines with the minor portion from the conduit 132 as described above.

The conduit 166 connected to the conduit 136 conducts a portion of the combined vaporized and super heated cryogenic fluid stream to the turbine 112 wherein it is utilized as fuel.

In operation of the system 90, the first portion of liquefied cryogenic fluid is heated and vaporized in the ambient water exchanger or exchangers 102 and superheated to as high a temperature level as possible by exchange of heat with the exhaust gases generated by the gas turbine 1 12. The minor portion of the vaporized cryogenic fluid is utilized to cool the input air to the turbine in order to increase the power output of the turbine. As described above for the system 10, the power output of the turbine 112 is advantageously utilized for operating an electric generator 168 which in turn provides the power for operating the pumps 94 and 106.

The vaporized and superheated cryogenic fluid stream resulting from the first portion of liquefied cryogenic fluid stream passes by way of conduit 136 to a contactor vessel 138. The vessel 138 may take a variety of forms, and functions simply to bring about intimate contact between the vaporized and superheated cryogenic fluid stream passing therethrough and the second portion of liquefied cryogenic fluid injected therein by way of conduit 100. As the liquefied cryogenic fluid stream is contacted by the superheated cryogenic fluid vapor, heat is transferred therebetween and the liquefied cryogenic fluid is vaporized and heated. The heat adsorbed by the vaporization and heating of the liquefied cryogenic fluid causes the composite stream to reach a temperature level below the temperature level of the superheated cryogenic fluid vapor entering the contactor 138. However, by controlling the flow rates of the first and second portions of liquefied cryogenic fluid and the temperature of the vaporized and superheated stream, the temperature level of the composite vapor stream passing from the vessel 138 by way of conduit 140 may be controlled at a desired level.

The use of the system 90 for carrying out the method of the present invention is particularly advantageous in that it provides a maximum degree of flexibility in operation. During the winter season, and depending upon the particular location of the source of ambient water, the temperature of the ambient water may be decreased appreciably. In this event, the heat available in the ambient water for heating and vaporizing the first portion of liquefied cryogenic fluid is reduced, and in order to maintain a minimum temperature drop in the ambient water, the flow rate of the first portion of liquefied cryogenic fluid passed to the ambient water heat exchanger or exchangers 102 must be reduced.-

However, in operation of the system 90, the volume and temperature of the exhaust gases generated by the turbine engine 112 remain constant and upon reduction of the flow rate of vaporized cryogenic fluid through the system, the temperature of the vaporized and superheated cryogenic fluid stream exiting the heat exchanger 116 increases. Thus, the heat contained in the vaporized and superheated cryogenic fluid stream entering the contactor 138 by way of the conduit 136 remains relatively constant even though the volume of the stream is decreased, and as a result, the rate of liquefied cryogenic fluid injected into the contactor 138 by way of the conduit 100 may be increased. That is, even though the temperature level of the ambient water decreases, and as a result, the first portion of liquefied cryogenic fluid passing through the system 90 v must be decreased in order to maintain the temperature drop in the ambient water at a minimum, the second portion of the liquefied cryogenic fluid stream may be increased so that the volume and temperature of the resulting composite stream exiting the contactor vessel 138 are substantially the same as was produced by the system 90 prior to the ambient water temperature decrease. Thus, by the present invention as carried out in the system 90, decreases in the temperature of the ambient water maybe automatically compensated for with the total volume of liquefied cryogenic fluid vaporized and superheated remaining relatively constant.

As described above for the system 10, the method of the present invention as carried out in the system 90 achieves low operating costs as compared to heretofore used methods and systems by the fact that the heat energy for superheating the cryogenic fluid stream as well as power for operating the various pumps required is produced within the system.

In order to present a clear understanding of the improved method of the present invention, the following examples are given.

EXAMPLE 1 A 1,723,000 lb/hr stream of liquefied natural gas (LNG) is vaporized and superheated by the system 10.-

The LNG stream is at a temperature of -260F, and is pumped from the storage tank 12 by the pump 14 to the heat exchanger 18 at a pump discharge pressure of 1000 psig. A total of 6,500 brake horsepower (bhp) is required for pumping the LNG. A 476,000 gpm stream of ambient water at a temperature of F is pumped by the pump 22 through the heat exchanger 18. A total of 18,600 bhp is required to pump the ambient water stream. For a 2F temperature drop in the water, 482,000,000 btu/hr are transferred from the ambient water stream to the LNG stream passing through the heat exchanger 18 causing the LNG to be vaporized and heated to a temperature of 50F. The vaporized natural gas stream at a temperature of -50F is conducted by conduit 34 to the conduits 35 and 37. A first portion of the vaporized natural gas (294,280 lb/hr) is passed by way of conduit 37 to the heat exchanger 32. A 780,000 lb/hr stream of exhaust gases at a temperature of 950F are conducted from the gas turbine 28 by way of conduit 30 to the heat exchanger 32. As the vaporized natural gas stream passes through the heat exchanger 32, 9,122,680 btu/hr are transferred from the turbine exhaust gases to the natural gas stream heating the natural gas stream to a temperature level of F. The heated natural gas stream is then passed by way of conduit 36 to the heat exchanger 38. A 767,800 lb/hr stream of combustion air at a temperature of 80F (50 percent saturated with water) passes by way of conduit 40 through the heat exchanger 38 and into the gas turbine 28 by way of conduit 42. As the combustion air passes through the heat exchanger 38, 12,190,000 btu/hr of heat is transferred from the air to the natural gas stream causing the air to be cooled to a temperature of 40F. 35,456 lb/hr of liquefied natural gas are combined with the natural gas stream as it passes through the tube banks 68, 70 and 74 of heat exchanger 38 and a 329,736 lb/hr combined stream of natural gas exits the heat exchanger 38 at a temperature of 4F. The second portion of the vaporized natural gas stream from the ambient water exchanger 18 (1,428,720 lb/hr) passes by way of conduit 35 to the heat exchanger 46.

The turbine exhaust gases from the heat exchanger 32 pass by way of duct 48 to the heat exchanger 46. 123,877,320 btu/hr of additional heat is transferred from the turbine exhaust gases to the natural gas stream passing through the heat exchanger 46 superheating the natural gas stream to a temperature of 75F. The spent turbine exhaust gases at a temperature of approximately 300F pass by way of the conduit 50 to the atmosphere. The first portion of natural gas at a temperature of 4F is combined with the second portion of natural gas at a temperature of 75F resulting in a 920 mmscf/d combined natural gas stream at a temperature of 60F. A 12,028 lb/hr portion of the superheated natural gas stream is conducted by way of conduit 54 to the gas turbine 28 and is utilized as fuel therefor. The gas turbine 28 develops a power output of 25,100 horsepower which is used to drive a conventional electric generator 56. The generator 56 produces 18,500 kilowatts of electric power which is sufficient to drive electric motors which in turn are used to drive the pumps 14 and 22.

Thus, it may be seen that the improved method of the present invention may be carried out in a system wherein ambient water is utilized with a minimum temperature drop therein. Further, the power for driving the various pumps used in the system is generated within the system.

EXAMPLE 2 A 1,723,000 lb/hr stream of liquefied natural gas (LNG) is vaporized and superheated in the system 90. The LNG stream is at a temperature of 260F and is pumped from the storage tank 92 by the pump 94 into the conduit 96 at a pump discharge pressure of 1000 psig. A total of 6,500 brake horsepower (bhp) is required for pumping the LNG. A 1,500,000 lb/hr first portion of the LNG is caused to pass by way of the conduit 98 to the ambient water heat exchanger 102. A 476,000 gpm stream of ambient water at a temperature of F is pumped by the pump 106 through the heat exchanger 102. A total of 18,600 bhp is required to pump the ambient water. For a 2F temperature drop in the water, 482,000,000 btu/hr are transferred from the ambient water stream to the LNG passing through the heat exchanger 102 resulting in the vaporization and heating of the LNG to a temperature of 0F. The vaporized natural gas at a temperature of 0F is conducted by the conduit 118 to the conduits 120 and 122. A minor portion of the vaporized natural gas (294,280 lb/hr) is passed by way of conduit 122 to the heat exchanger 126. A 767,800 lb/hr stream of combustion air at a temperature of F (50 percent saturated with water) passes by way of conduit 128 through the heat exchanger 126 and into the gas turbine 112 by way of conduit 130. As the combustion air passes through the heat exchanger 126, 12,190,000 btu/hr of heat is transferred from the air to the natural gas stream causing the air to be cooled to a temperature of 40F. 35,456 lb/hr of liquefied natural gas are combined with the gas stream as it passes through the tube banks 144, 146 and 150 of the heat exchanger 126 and a 329,736 lb/hr combined stream of natural gas exits the heat exchanger 126 at a temperature of 6F.

The major portion of the vaporized natural gas stream from the ambient water exchanger 102 (1,205,720lb/hr) passes by way of conduit to the heat exchanger 116. A 780,000 lb/hr stream of turbine exhaust gases at a temperature of 950F are conducted from the gas turbine 112 by way of conduit 114 to the heat exchanger 116. As the major portion of the vaporized natural gas stream passes through the heat exchanger 116, 133,000,000 btu/hr of heat is transferred from the turbine exhaust gases to the natural gas stream superheating the natural gas stream to a temperature of 168F. The spent turbine exhaust gases at a temperature of approximately 300F pass by way of the conduit 124 to the atmosphere. The minor portion of natural gas at a temperature of 6F is combined with a major portion of natural gas at a temperature of 168F resulting in an 812 mmscf/d combined natural gas stream at a temperature of F. A 12,028 lb/ hr portion of the combined stream is conducted by way of conduit 166 to the gas turbine 112 and is utilized as fuel therefor. The remaining combined stream (approximately 1,523,000 lb/hr) at a temperature of 135F is conducted by the conduit 136 to the contactor vessel 138. The second portion of the LNG stream (187,544 lb/hr) at a temperature of 260F is injected into the contactor 138 by way of the conduit 100. The LNG stream is vaporized and heated by heat exchange with the 135F natural gas stream within the contactor 138 resulting in a 920 mmscf/d composite natural gas stream at a temperature of 60F.

The gas turbine 112 develops a power output of ap- I combining a quantity of liquefied cryogenic fluid proximately 25,l horsepower which is used to drive the pumps 94 and 106.

' In the event the temperature of the ambient water utilized in the system 90 decreases from a temperature of 70F to a temperature of 50F and in order to maintain the temperature drop of the water at 2F, the first portion of LNG passed by way of the conduit 98 to the heat exchangers 102 must be reduced by approximately 13 percent. However, the second portion of LNG injected into the contactor 138 can be increased by a factor of 5 percent due to the heat content of the superheated natural gas passing into the contactor 138 by ,way of the conduit 136 remaining relatively constant,

resulting in a total vaporized and superheated natural gas outflow from the system 9.0 of 8 percent less than the outflow when ambient water at a temperature of 70 F is utilized.

Thus, it may be seen that for small decreases in the ambient water temperature, i.e., 5 to 10F, the outflow of vaporized and superheated natural gas from the system 90 may be maintained relatively constant.

The present invention, therefore, is well adapted to carry out the objects and attain the ends and advantages mentioned as well as those inherent therein.

While presently preferred systems for carrying out the method of the present invention are given for the purpose of disclosure, numerous changes can be made which will readily suggest themselves to those skilled in the art and which are encompassed within the spirit of the invention disclosed herein.

What is claimed is:

1. A method of continuously vaporizing and superheating a stream of liquefied cryogenic fluid for an ultimate use comprising the steps of:

a. passing said stream of liquefied cryogenic fluid in heat exchange relationship with a stream of ambient water so that said cryogenic fluid stream is heated and vaporized;

b. dividing said heated and vaporized cryogenic fluid stream into first and second portions;

c. passing the first portion of said vaporized cryogenic fluid stream in heat exchange relationship with input combustion air to a gas turbine engine so that said air is cooled and the power output of said turbine engine increased;

d. passing the second portion of said vaporized cryogenic fluid stream in heat exchange relationship with the exhaust gases generated by said gas turbine engine so that the second portion is superheated to a predetermined temperature level;

e. combining said first and second portions of said vaporized cryogenic fluid stream so that a vaporized cryogenic fluid stream superheated to a desired temperature level is produced; and

f. utilizing the power output of said gas turbine engine for carrying out step (a).

2. The method of claim 1 which is further characterized to include the steps of:

passing the first portion of said vaporized cryogenic fluid stream in heat exchange relationship with said turbine engine input air in successive serially connected stages so that the formation of ice from water vapor contained in the air is maintained at a minimum; and

with the vaporized cryogenic fluid exiting from each of said heat exchange stages so that it is cooled prior to passing through the next successive stage. 7 3. The method of claim 2 which is further characterized to include the step of passing the first portion of said vaporized cryogenic fluid stream in heat exchange relationship with the turbine engine exhaust gases so that the first portion is superheated to a predetermined temperature level prior to passing said stream in heat exchange relationship with said turbine engine input air.

4. The method of claim 3 wherein the liquefied cryogenic fluid stream is liquefied natural gas.

5. The method of claim 4 wherein the ambient water is sea water.

6. The method of claim 5 wherein a portion of the produced superheated natural gas is utilized as fuel for said turbine.

7. A method of continuously vaporizing and superheating a stream of liquefied cryogenic fluid for an ultimate use comprising the steps of:

a. pumping said stream of liquefied cryogenic fluid through a first heat exchanger;

b. pumping a stream of ambient water through said first heat exchanger so that heat is transferred from the water to said liquefied cryogenic fluid causing the cryogenic fluid to be heated and vaporized;

c. dividing the heated and vaporized cryogenic fluid stream into first and second portions;

d. passing the first portion of said vaporized cryogenic fluid stream through a second heat exchanger;

e. passing input combustion air to a gas turbine engine through said second heat exchanger in heat exchange relationship with the first portion of said vaporized cryogenic fluid stream so that the input air is cooled and the power output of said turbine is increased;

f. passing the second portion of said vaporized cryogenic fluid stream through a third heat exchanger;

g. passing the exhaust gases generated by said gas turbine through said third heat exchanger in heat exchange relationship with the second portion of the vaporized cryogenic fluid stream so that 'the second portion is superheated to a predetermined temperature level;

h. combining the first and second portions of said vaporized cryogenic fluid stream so that a vaporized cryogenic fluid stream superheated to a desired temperature level is produced; and

i. utilizing the power output of said gas turbine engine for pumping the streams of liquefied cryogenic fluid and ambient water.

8. The method of claim 7 which is further characterized to include the steps of:

passing the first portion of said vaporized cryogenic fluid stream in heat exchange relationship with said turbine engine input air in successive serially connected stages so that the formation of ice from water vapor contained in said air is maintained at a minimum; and

combining a quantity of liquefied cryogenic fluid with the vaporized cryogenic fluid exiting from each of said heat exchange stages so that it is cooled prior to passing through the next successive stage.

9. The method of claim 8 which is further characterized to include the step of passing the first portion of said vaporized cryogenic fluid stream in heat exchange relationship with the turbine engine exhaust gases so that the first portion is superheated to a predetermined temperature level prior to passing said stream in heat exchange relationship with said turbine input air.

10. The method of claim 9 wherein the liquefied cryogenic fluid is liquefied natural gas.

11. The method of claim 10 wherein said ambient water is sea water.

12. The method of claim 11 wherein a portion of the produced superheated natural gas is utilized as fuel for said gas turbine.

13. A method of continuously vaporizing and superheating a stream of liquefied cryogenic fluid for an ultimate use comprising the steps of:

a. dividing the liquefied cryogenic fluid stream into first and second portions;

b. passing the first portion of said liquefied cryogenic fluid stream in heat exchange relationship with a stream of ambient water so that said first portion is heated and vaporized;

c. dividing said heated and vaporized first portion into major and minor portions;

d. passing the minor portion of said vaporized cryogenic fluid stream in heat exchange relationship with input combustion air to a gas turbine engine so that said air is cooled and the power output of the gas turbine is increased;

. passing the major portion of said vaporized cryogenic fluid stream in heat exchange relationship with the exhaust gases generated by said gas turbine so that the major portion of said vaporized cryogenic fluid stream is superheated",

f. combining the minor portion and the superheated major portion of said vaporized cryogenic fluid stream so that a vaporized and superheated combined cryogenic fluid stream is formed from said first portion ofliquefied cryogenic fluid; and

. combining the second portion of said liquefied cryogenic fluid stream with said vaporized and superheated combined cryogenic fluid stream so that the second portion of said liquefied cryogenic fluid is vaporized and a composite stream of vaporized cryogenic fluid is produced at a desired level of superheat.

14. The method of claim 13 which is further characterized to include the steps of:

passing the minor portion of said vaporized cryogenic fluid stream in heat exchange relationship with said turbine engine input air in successive serially connected stages so that the formation of ice from water vapor contained in the air is maintained at a minimum; and combining a quantity of liquefied cryogenic fluid with the vaporized cryogenic fluid exiting from each of said heat exchange stages so that it is cooled prior to passing through the next successive sta e. 15. 1%? method of claim 14 which is further characterized to include the step of passing the minor portion of said vaporized cryogenic fluid in heat exchange relationship with said turbine exhaust gases so that first 

1. A method of continuously vaporizing and superheating a stream of liquefied cryogenic fluid for an ultimate use comprising the steps of: a. passing said stream of liquefied cryogenic fluid in heat exchange relationship with a stream of ambient water so that said cryogenic fluid stream is heated and vaporized; b. dividing said heated and vaporized cryogenic fluid stream into first and second portions; c. passing the first portion of said vaporized cryogenic fluid stream in heat exchange relationship with input combustion air to a gas turbine engine so that said air is cooled and the power output of said turbine engine increased; d. passing the second portion of said vaporized cryogenic fluid stream in heat exchange relationship with the exhaust gases generated by said gas turbine engine so that the second portion is superheated to a predetermined temperature level; e. combining said first and second portions of said vaporized cryogenic fluid stream so that a vaporized cryogenic fluid stream superheated to a desired temperature level is produced; and f. utilizing the power output of said gas turbine engine for carrying out step (a).
 2. The method of claim 1 which is further characterized to include the steps of: passing the first portion of said vaporized cryogenic fluid stream in heat exchange relationship with said turbine engine input air in successive serially connected stages so that the formation of ice from water vapor contained in the air is maintained at a minimum; and combining a quantity of liquefied cryogenic fluid with the vaporized cryogenic fluid exiting from each of said heat exchange stages so that it is cooled prior to passing through the next successive stage.
 3. The method of claim 2 which is further characterized to include the step of passing the first portion of said vaporized cryogenic fluid stream in heat exchange relationship with the turbine engine exhaust gases so that the first portion is superheated to a predetermined temperature level prior to passing said stream in heat exchange relationship with said turbine engine input air.
 4. The method of claim 3 wherein the liquefied cryogenic fluid stream is liquefied natural gas.
 5. The method of claim 4 wherein the ambient water is sea water.
 6. The method of claim 5 wherein a portion of the produced superheated natural gas is utilized as fuel for said turbine.
 7. A method of continuously vaporizing and superheating a stream of liquefied cryogenic fluid for an ultimate use comprising the steps of: a. pumping said stream of liquefied cryogenic fluid through a first heat exchanger; b. pumping a stream of ambient water through said first heat exchanger so that heat is transferred from the water to said liquefied cryogenic fluid causing the cryogenic fluid to be heated and vaporized; c. dividing the heated and vaporized cryogenic fluid stream into first and second portions; d. passing the first portion of said vaporized cryogenic fluid stream through a second heat exchanger; e. passing input combustion air to a gas turbine engine through said second heat exchanger in heat exchange relationship with the first portion of said vaporized cryogenic fluid stream so that the input air is cooled and the power output of said turbine is increased; f. passing the second portion of said vaporized cryogenic fluid stream through a third heat exchanger; g. passing the exhaust gases generated by said gas turbine through said third heat exchanger in heat exchange relationship with the second portion of the vaporized cryogenic fluid stream so that the second portion is superheated to a predetermined temperature level; h. combining the first and second portions of said vaporized cryogenic fluid stream so that a vaporized cryogenic fluid stream superheated to a desired temperature level is produced; and i. utilizing thE power output of said gas turbine engine for pumping the streams of liquefied cryogenic fluid and ambient water.
 8. The method of claim 7 which is further characterized to include the steps of: passing the first portion of said vaporized cryogenic fluid stream in heat exchange relationship with said turbine engine input air in successive serially connected stages so that the formation of ice from water vapor contained in said air is maintained at a minimum; and combining a quantity of liquefied cryogenic fluid with the vaporized cryogenic fluid exiting from each of said heat exchange stages so that it is cooled prior to passing through the next successive stage.
 9. The method of claim 8 which is further characterized to include the step of passing the first portion of said vaporized cryogenic fluid stream in heat exchange relationship with the turbine engine exhaust gases so that the first portion is superheated to a predetermined temperature level prior to passing said stream in heat exchange relationship with said turbine input air.
 10. The method of claim 9 wherein the liquefied cryogenic fluid is liquefied natural gas.
 11. The method of claim 10 wherein said ambient water is sea water.
 12. The method of claim 11 wherein a portion of the produced superheated natural gas is utilized as fuel for said gas turbine.
 13. A method of continuously vaporizing and superheating a stream of liquefied cryogenic fluid for an ultimate use comprising the steps of: a. dividing the liquefied cryogenic fluid stream into first and second portions; b. passing the first portion of said liquefied cryogenic fluid stream in heat exchange relationship with a stream of ambient water so that said first portion is heated and vaporized; c. dividing said heated and vaporized first portion into major and minor portions; d. passing the minor portion of said vaporized cryogenic fluid stream in heat exchange relationship with input combustion air to a gas turbine engine so that said air is cooled and the power output of the gas turbine is increased; e. passing the major portion of said vaporized cryogenic fluid stream in heat exchange relationship with the exhaust gases generated by said gas turbine so that the major portion of said vaporized cryogenic fluid stream is superheated; f. combining the minor portion and the superheated major portion of said vaporized cryogenic fluid stream so that a vaporized and superheated combined cryogenic fluid stream is formed from said first portion of liquefied cryogenic fluid; and g. combining the second portion of said liquefied cryogenic fluid stream with said vaporized and superheated combined cryogenic fluid stream so that the second portion of said liquefied cryogenic fluid is vaporized and a composite stream of vaporized cryogenic fluid is produced at a desired level of superheat.
 14. The method of claim 13 which is further characterized to include the steps of: passing the minor portion of said vaporized cryogenic fluid stream in heat exchange relationship with said turbine engine input air in successive serially connected stages so that the formation of ice from water vapor contained in the air is maintained at a minimum; and combining a quantity of liquefied cryogenic fluid with the vaporized cryogenic fluid exiting from each of said heat exchange stages so that it is cooled prior to passing through the next successive stage.
 15. The method of claim 14 which is further characterized to include the step of passing the minor portion of said vaporized cryogenic fluid in heat exchange relationship with said turbine exhaust gases so that first portion is superheated to a predetermined temperature level prior to passing said stream in heat exchange relationship with said turbine engine input air.
 16. The method of claim 15 wherein the liquefied cryogenic fluid stream is liquefied natural gas.
 17. The method of claim 16 wherein the ambient water is sea water. 